. . . . . . . . . "Lower paleozoic carbonate rocks in Maryland and Pennsylvania"@en . . . . . . . "Lower Paleozoic carbonate rocks in Maryland and Pennsylvania"@en . . . . . "Lower paleozoic carbonate rocks in Maryland and Pennsylvania : Guidebook 3, field trip - 1960 annual convention, American Association of Petroleum Geologists, Society of Economic Paleontologists and Mineralogists"@en . . . . . "From 230 to 570 million years ago" . . . .